In recent years, lithium secondary batteries have been widely used as driving power supplies for small-size electronic devices such as mobile telephones, notebook-size personal computers and the like, and for power supplies for electric vehicles and for electric power storage.
A lithium secondary battery is mainly constituted of a positive electrode and a negative electrode containing a material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution containing a lithium salt. For the nonaqueous electrolytic solution, used are carbonates such as ethylene carbonate (EC), propylene carbonate (PC), etc.
As the negative electrode for the lithium secondary battery, known are metal lithium, and metal compounds (metal elemental substances, oxides, alloys with lithium, etc.) and carbon materials capable of absorbing and releasing lithium. In particular, nonaqueous electrolytic solution-containing lithium secondary batteries using a carbon material capable of absorbing and releasing lithium such as coke, graphite (artificial graphite, natural graphite) or the like have been widely put into practical use.
The above-mentioned negative electrode materials store and release lithium and electron at a low potential on the same level as that of lithium metal, and therefore especially at high temperatures, they have a possibility of reduction and decomposition of many solvents, and irrespective of the type of the negative electrode material, the solvent in the electrolytic solution may be partly reductively decomposed on a negative electrode, therefore bringing about some problems in that the resistance may increase owing to deposition of decomposed products, that the battery may be swollen owing to gas generation through solvent decomposition and that lithium ion movement may be retarded thereby worsening the battery characteristics such as cycle property and the like.
On the other hand, a material capable of storing and releasing lithium such as LiCoO2, LiMn2O4, LiNiO2, LiFePO4 or the like that is used as a positive electrode material stores and releases lithium and electron at a high voltage of 3.5 V or more based on lithium, and therefore has a possibility of oxidation and decomposition of many solvents. In addition, irrespective of the type of the positive electrode material, the solvent in the electrolytic solution may be partly oxidized and decomposed on a positive electrode, therefore bringing about some problems in that the resistance may increase owing to deposition of decomposed products on the surface of the positive electrode, that the battery may be swollen owing to gas generation through solvent decomposition and that lithium ion movement may be retarded thereby worsening the battery characteristics such as cycle property and the like.
As a lithium primary battery, for example, there is known a lithium primary battery comprising manganese dioxide or graphite fluoride as the positive electrode and a lithium metal as the negative electrode, and this is widely used as having a high energy density. It is desired to inhibit the increase in the internal resistance of the battery during long-term storage and to improve the long-term storage property thereof at high temperatures.
Recently, further, as a novel power source for electric vehicles or hybrid electric vehicles, electric storage devices have been developed, for example, an electric double layer capacitor using activated carbon or the like as the electrode from the viewpoint of the output power density thereof, and a so-called hybrid capacitor comprising a combination of the electric power storage principle of a lithium ion secondary battery and that of an electric double layer capacitor (an asymmetric capacitor where both the capacity by lithium absorption and release and the electric double layer capacity are utilized) from the viewpoint of both the energy density and the output power density thereof; and it is desired to improve the battery performance of the capacitors such as the cycle property at high temperatures and the high-temperature storage property thereof.
Patent Reference 1 discloses a lithium secondary battery using a nonaqueous electrolytic solution that contains a nonaqueous solvent containing a lactone compound and a nitrogen-having heterocyclic compound such as 1-methyl-2-pyrrolidone, saying that the charge-discharge efficiency and the capacity retention after high-temperature charging and storage of the lactone compound-containing nonaqueous electrolytic solution is improved. Patent Reference 1 shows extremely a large number of nitrogen-having heterocyclic compounds; and in its paragraph [0017], 1,3-dimethylimidazolidine-2,5-dione and 1,3-diethylimidazolidine-2,5-dione are shown. However, addition of such a hydantoin compound is not concretely described at all in Patent Reference 1. No substantial investigation about it is made therein.
Patent Reference 2 discloses a nonaqueous electrolytic solution comprising a succinimide derivative added to a nonaqueous solvent containing an asymmetric carbonate, saying that the cycle property at 20° C. and the capacity retention after high-temperature charging and storage of the lithium secondary battery shown therein are good.
Patent Reference 3 discloses a nonaqueous electrolytic solution battery in which the nonaqueous electrolyte contains 1,3-dimethyl-2-imidazolidinone, saying that the load characteristic, the cycle property at 23° C. and the capacity retention after high-temperature charging and storage of the battery have been improved.
[Patent Reference 1] JP-A 2003-7333
[Patent Reference 2] JP-A 2003-151622
[Patent Reference 3] JP-A 11-273728